Plastic containers, for an extensive period of time, have found widespread use in society for holding a vast array of goods. In fact, such containers have become so omnipresent that their disposal now poses a substantial problem. Society no longer wishes to place the used containers into the very limited landfill left to it.
Accordingly, recent years have witnessed a substantial effort to recycle plastic containers. This would accomplish several desirable results. First, it will help save the limited resources of our planet for future generations. Furthermore, recycling will have the obvious effect of conserving the landfill that remains available.
However, much plastic finds use in containers that hold food items. Most desirably, recycling must employ previously used plastic in new food containers. In fact, various legislative bodies are considering the requirement that a certain portion, generally around 25 percent, of all containers, including specifically those intended for food, must consist of recycled plastic.
The problem with utilizing recycled plastic in food containers results from the fact that these containers have previously held all types of materials. Many of these materials, for one reason or another, constitute contaminants should they enter food items above a negligible concentration.
The essential problem arises, of course, from the fact that contaminants found in recycled plastic, because of their previous use, could leach out of the new containers and into the food. A brief acknowledgment of the wide variety of uses that plastic containers find shows the magnitude of the concern. Thus, plastic holds everything from food itself including milk to chemicals such as herbicides and insecticides that could prove toxic to humans and other animals.
Consumers may exacerbate the problem. After emptying the contents of a plastic container, they may reuse it to hold chemicals of an entirely different, and perhaps more ominous nature, than the originally held ingredients. These may include everything from used motor oil to all types of poisons. These containers too, after their initial and subsequent uses by the consumer, may enter the recycling stream. Any use of the plastic from these containers in recycling must provide absolute assurance that whatever such containers may have held will pose no danger to food consumed by individuals.
The United States Food and Drug Administration (FDA) has determined that a contaminant on a level below 0.5 parts per billion in ingested food presents substantially no risk of harm to humans. Thus, any use of recycled plastic in containers must provide assurance that it will not cause the exceeding of that level of undesired foreign substances in a person's diet. In particular, the FDA requires a demonstration, under adverse conditions, of protection against four classes of chemicals; these classes include volatile and nonvolatile, polar and nonpolar organic compounds, as well as a heavy-metal salt and a polymer-specific chemical. Thus, the intended manner of use of post-consumer recycled ("PCR") plastic must show that it will not introduce more than the indicated amount of contaminant into food.
One particular method of employing recycled resin involves placing a barrier layer on the inside of the previously used plastic. Such a barrier must prevent the passage of contaminants into a container's interior holding a food-like substance, generally an ethyl alcohol solution. One test for establishing this barrier capacity involves placing the container made of or with the proposed barrier and containing the alcohol solution in essentially pure contaminant. Alternatively, the test may involve placing the contaminant on the exterior of a container with the barrier material.
The need for a barrier, however, only exists when the contaminant level within the recycled plastic exceeds certain maximum levels. Below those levels, as suggested in the FDA Points to Consider for the Use of Recycled Plastics in Food Packaging: Chemistry Considerations (May, 1992), an insufficient amount of contaminant could possibly leach into the container's contents to create a health risk. The calculation assumes that all of a contaminant in the PCR resin will enter the container's food. In the case of polyolefins, that contaminant level currently stands at 48 parts per billion (ppb.) for a container having a PCR layer 0.020 inch thick. A thicker layer will have more contaminant and cause the permissible level to proportionately decline. Several layers with PCR introduce additive quantities of the contaminant. This has special significance since much PCR resin has a majority of polyethylene. Polyethylene terepthalate ("PET"), by comparison, may have a residue of 215 ppb. Between those two sit polystyrene at 180 ppb. and polyvinyl chloride at 90 ppb. Decreasing the PCR layer thickness increases the allowable contaminant level. Only the thickness of the layers within the PCR are considered in this determination. Diluting the PCR with virgin resin proportionately increases the permissible contaminant level in the unmixed PCR.
The current recycling process does appear to reduce the concentration of some contaminants in previously used resin. However, the present treatment of recycled materials does not seem to currently offer the hope of reducing the residue level of all contaminant types to below these limits.
Accordingly, the search continues for barriers that will permit the use, and perhaps the required use, of recycled plastic for food containers. Yet, the barrier should not prohibitively increase the cost of the resulting containers.